Operating a Crossover with One Turnout Motor
by Ångström
[This is an idiosyncratic view of the solution to a problem common to most model railway layouts – how to economise on expensive points or turnout motors. But it is such a good solution that I want to share it with you all. PK]
Someone asked a question in the BRMA Email Group as to whether a crossover could be operated from one turnout motor. Of the replies that were forthcoming, the answer was a resounding yes. However, there were no suggestions as to how the mechanical linkages should be made, so I thought a short article on the subject might be appropriate.
Actually I have never used a points motor in my life and never will, but I have operated a crossover with ONE mechanical points lever. The mechanics of the system, whether the prime mover is an electric motor or a human hand are the same, so here goes.
The first problem to be encountered is that the tie bars of the two points that make up the crossing must move in opposite directions. This is overcome by using a centre-pivoted lever with one tie bar connected to each end of the lever. The centre bearing of this lever is, of course, fixed to the baseboard. This is the right-hand lever in the diagram. If this were the only problem, the motor (or other prime mover) could simply be connected to either end of the lever.
The second problem is that the amount of travel of the two tie bars might be marginally different or, in addition, the pin joints on each end of the lever, might have different amounts of slop. This problem is overcome by incorporating a compensating lever (the left-hand one in the diagram) having a pivot connected to the motor's moving rod. The two levers are not rigidly connected together, being linked via a pin joint only.
The third problem is that the amount of movement of the motor is probably much larger than that required by either tie bar. This problem of course exists even if the motor is driving just one tie bar. Rather than building in some complicated spring device to take up the excessive movement of the motor, motion can be lost simply by moving the pivot point of the right-hand lever more to the right. This is shown on the diagram as a series of holes in the lever in question. By trial and error, the fixed pivot can be connected to any one of these holes until perfect operation is forthcoming.
As to where all these levers should be located on the layout, that is up to the individual to decide. However, I am a strong advocate of putting them on the top of the baseboard and hiding them in a building or in some sort of covered walkway.
Amended 30-6-00